1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image on a recording medium using a recording technique such as an electrophotographic recording process.
2. Description of the Related Art
Replaceable units are mounted in an image forming apparatus such as a printer or a copier which forms an image on a recording medium using an electrophotographic recording process. The replaceable units are, for example, a cartridge in which a photoreceptor is housed and a fixing unit, and replacement of these units allows the photoreceptor and a roller such as a fixing roller to be replaced with new ones. The photoreceptor and the fixing roller in these units are driven by a motor provided in the main assembly of the image forming apparatus. In order to transmit the power of the motor to the roller, an image forming main assembly of the apparatus-side gear needs to engage with a unit-side gear. For apparatus design reasons, the unit-side gear is forced to have a cantilevered configuration. When a gear with a cantilevered configuration is driven, the shaft of the gear is likely to be deflected to cause a possible jumping phenomenon, leading to the risk of stoppage of the apparatus or an abnormal sound.
In association with this problem, a configuration is known in which, for example, to allow transmission of driving from the main assembly of the apparatus to the removable unit, the unit is provided with a shaft with a twisted polygonal columnar protrusion, whereas the main assembly of the apparatus includes a coupling shaft that engages with the twisted polygonal column to transmit driving (Japanese Patent Application Laid-open No. H10-104905).
However, the configuration disclosed in Japanese Patent Application Laid-open No. H10-104905 involves an increased size of the apparatus due to the use of the coupling member. Furthermore, in an image forming apparatus that enables duplex printing, for example, a reverse roller that reverses a conveying direction of a recording medium needs to rotate in a normal direction and in a reverse direction. However, the configuration disclosed in Japanese Patent Application Laid-open No. H10-104905 can deal only with rotation in one direction and is thus unsuitable for a drive member that needs to rotate in both directions.